16 000 Chrysomyia albiceps and 52 000 C. marginalis adults were radioactively labelled with 32P-orthophosphate and released in the northern Kruger National Park, South Africa. After a 1-week dispersal period 69 baited blow-fly traps were placed in different habitat types and at varying distances around the release point. C. albiceps were subsequently found to have covered up to 37.5 km and C. marginalis 63.5 km, suggesting dispersal rates per day of 2.20 km and 2.35 km for the 2 species, respectively. Calculation of density using the Lincoln Index yielded estimates per hectare of 7.56 C. albiceps and 29.03 C. marginalis. Both species were trapped more numerously in forested environments than in open scrub, and both avoided arid scrubland.